I've been getting a P0031 Ho2S bank 1 sen 1 heater circuit low check engine light on my 02 WRX for about a week now. After looking around the forums the general consensus is that its either the wiring for the A/F sensor or the sensor itself has gone bad.

Since the part from subaru ($252 ouch~) contains both the sensor and wires it really doesn't matter which one is bad i suppose.

Anyway, on to my question. Can someone tell me where exactly this sensor is located, and how big a pain in the ass it is to swap it out? From reading the forums i have read that its either on the up pipe, or my header on the passenger side of the car, and not exactly needs to come off in order to get to it.

I'd like to avoid taking it to Subaru to get it replaced, so any information as in depth as possible would be greatly appreciated.

Thanks in advance for any help.